Numerous procedures have been developed for treating occluded blood vessels to allow blood to flow without obstruction. Such procedures usually involve the percutaneous introduction of an interventional device into the lumen of the artery, usually by a catheter. One widely known and medically accepted procedure is balloon angioplasty in which an inflatable balloon is introduced within the stenosed region of the blood vessel to dilate the occluded vessel. The balloon dilatation catheter is initially inserted into the patient's arterial system and is advanced and manipulated into the area of stenosis in the artery. The balloon is inflated to compress the plaque and press the vessel wall radially outward to increase the diameter of the blood vessel, resulting in increased blood flow. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient's vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
Another procedure is laser angioplasty which uses a laser to ablate the stenosis by superheating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed body vessel in which cutting blades are rotated to shave the deposited plaque from the arterial wall. A catheter is usually used to capture the shaved plaque or thrombus from the bloodstream during this procedure.
In the procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent can be crimped tightly onto the balloon portion of the catheter and transported in its delivery diameter through the patient's vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter.
The above non-surgical interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem which can become associated with all of these non-surgical procedures, namely, the potential release of embolic debris into the bloodstream that can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of frangible plaque that can travel downstream and lodge somewhere in the patient's vascular system. Pieces of plaque are sometimes generated during a balloon angioplasty procedure and released into the bloodstream. This is particularly true when the procedure is performed in a saphenous vein graft (SVG).
Additionally, while complete vaporization of plaque is the intended goal during laser angioplasty, sometimes particles are not fully vaporized and enter the bloodstream. Likewise, not all of the emboli created during an atherectomy procedure may be drawn into the catheter and, as a result, enter the bloodstream.
When any of the above-described procedures are performed in the carotid arteries, the release of emboli into the circulatory system can be extremely dangerous and sometimes fatal to the patient. Debris carried by the bloodstream to distal vessels of the brain can cause cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although cerebral percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been somewhat limited due to the justifiable fear of an embolic stroke occurring should embolic debris enter the bloodstream and block vital downstream blood passages.
Medical devices have been developed to address the problem created when debris or fragments enter the circulatory system following vessel treatment using any one of the above-identified procedures. One approach is to cut the debris into minute sizes which pose little chance of becoming occluded in major vessels within the patient's vasculature. However, it is often difficult to control the size of the fragments that are formed. So the potential risk of vessel occlusion still exists, making such a procedure in the carotid arteries a high-risk proposition.
Other techniques include the use of catheters with a vacuum source that provides temporary suction to remove embolic debris from the bloodstream. On the other hand, there can be complications associated with such systems if the vacuum catheter does not remove all of the embolic material from the bloodstream. Also, a powerful suction could cause trauma to the patient's vasculature.
Another technique which has had some success deploys a filter or trap downstream from the treatment site to capture embolic debris before they reach the smaller blood vessels downstream. The placement of a filter in the patient's vasculature during treatment of the vascular lesion can reduce the presence of the embolic debris in the bloodstream. Such embolic filters are usually delivered in a collapsed position through the patient's vasculature and then expanded to trap the embolic debris. Some of these embolic filters are self-expanding and rely on a restraining sheath that maintains the expandable filter in the collapsed position until it is ready to be expanded at the target site within the patient's vasculature. At the target site, the physician retracts the proximal end of the restraining sheath to expose the expandable filter, allowing the filter to self-expand at the desired location. Once the procedure is completed, the filter can be collapsed. The filter with the trapped embolic debris can then be removed from the vessel.
While a filter can be effective in capturing embolic material, the filter still needs to be collapsed and removed from the vessel. During these steps, there is a possibility that trapped embolic debris can backflow through the inlet opening of the filter and re-enter the bloodstream. Therefore, it is important that any captured embolic debris remain trapped within the filter so that particles are not inadvertently released back into the body vessel.
Some prior art expandable filters are attached to the distal end of a guide wire or guide wire-like member which allows the filtering device to be steered in the patient's vasculature as the guide wire is positioned by the physician. Once the guide wire is in proper position in the vasculature, the embolic filter is deployed to capture embolic debris. The guide wire can then be used by the physician to deliver interventional devices, such as a balloon angioplasty dilatation catheter or a stent delivery catheter, to perform the interventional procedure in the area of treatment. After the procedure is completed, a recovery sheath is delivered over the guide wire using over-the-wire techniques to collapse the expanded filter for removal from the patient's vasculature.
When a combination of an expandable filter and a guide wire is used, the expandable filter portion should be flexible in order to negotiate the often tortuous anatomy through which it is being delivered. An expandable filter that is too stiff could prevent the device from reaching the desired deployment position within the patient's vasculature. As a result, there is a need to increase the flexibility of the expandable filter without compromising its structural integrity once in position within the patient's body vessel. Also, while it is beneficial if the area of treatment is located in a substantially straight portion of the patient's vasculature, sometimes the area of treatment is at a curved portion of the body vessel which can be problematic to the physician when deploying the expandable filter. If the expandable filter portion is too stiff, it is possible that the filter may not fully deploy within the curved portion of the body vessel. As a result, gaps between the filter and vessel wall can form that may permit some embolic debris to pass therethrough. Therefore, the filtering device should be sufficiently flexible to be deployed in, and to conform to, a tortuous section of the patient's vasculature when needed.
Expandable filters can be provided with some increased flexibility by forming the struts of the filter assembly from relatively thin material. The use of thin material, however, often reduces the radiopacity of the expandable filter. This often makes it difficult for the physician to visualize the filter during deployment. Conversely, the use of thicker materials, which can promote radiopacity of the expandable filter, usually reduces its flexibility and may impair the deliverability of the expandable filter within the patient.
In addition, nickel-titanium alloys have been used to make embolic filters. But visualization of filters made from a nickel-titanium alloy, which has relatively low radiopacity as compared to other metallic materials, is also difficult during fluoroscopy.
What has been needed is an expandable filter assembly having high flexibility with sufficient strength and radiopacity to be successfully deployed within a patient's vasculature to collect embolic debris. The present invention disclosed herein satisfies these and other needs.